The present invention relates to a radiator for motor cars and its objective is to prevent the stress and corrosion crackings of the resinous radiator to improve its reliability in an economical manner.
In general, the radiator for motor cars is one for cooling the engine section. The cooling is carried therein out by allowing the heat-exchanging medium, for example, water or an anti-freeze fluid wherein glycol or glycol ether is added to water, to circulate between the radiator and the engine section and allowing the anti-freeze medium, whose temperature increases at the engine section, to heat-exchange with outside air in the radiator. Usually, the radiator is constructed, as shown in FIG. 1, in such a way that corrugated fins (2) made of copper are fitted by brazing between many brass tubes (1), through which the medium passes, to form a core (3), the brass tube plates (4) and (4') are provided at both ends of the tubes (1) of said core (3), and the open ends of the brass tanks (5) and (5') are fitted by brazing to said tube plates (4) and (4').
However, in order to lighten the car, a resinous radiator has been used. For example, as shown in FIG. 2, the peripheral portion of the tube plates (4) and (4') is bent to form a concave groove (6) opening to the outside, an elastic seal member (7) is provided in said concave groove (6) to insert the flange portion (5a) of the resinous tank (5), and the upper portion of the outer side (8) of the concave groove (6) is bent inwards to securely attache the tank.
Usually, for the tank, reinforced plastics, such as nylon filled with glass fibers etc., are used, and, for the tube plate, .alpha. brass plate (thickness: 0.5-1.2 mm) containing 30 to 35 wt. % Zn is used. The .alpha. brass has excellent strength and a good workability and is known as the most inexpensive alloy. However, with a resinous radiator cracking occurs starting from the inner portion during use. The cracking occurs mainly at the bottom portion of the concave groove and becomes pronounced particularly when the tube plate is made thin in order to lighten the car.
It has been known that the aforementioned cracking is a kind of stress and corrosion cracking (hereinafter abbreviated as SCC) and occurs as a brittle fracture along the particle boundary of brass, and that, though SCC is said to be caused usually with ammonia, even with the anti-freeze medium, in particular, the medium deficient in the component of rust inhibitor or general water for use, SCC becomes active due to the high temperature condition at the time of the running of radiator. SCC in a radiator using a resinous tank has been prevented and its reliability has been improved by the practice of this invention.